US20120137962A1

US20120137962A1 - Gas supply device for use in crystal-growing furnace

Info

Publication number: US20120137962A1
Application number: US12/960,045
Authority: US
Inventors: Jyh-Chen Chen; Ying-Yang Teng; Chung-Wei LU; Hsueh-I Chen
Original assignee: National Central University
Current assignee: National Central University
Priority date: 2010-12-03
Filing date: 2010-12-03
Publication date: 2012-06-07

Abstract

The present invention relates to a gas supply device for use in a crystal-growing furnace. The gas supply device has an insulation layer enclosing a crucible, a gas inlet mounted in the insulation layer, and a gas exit formed in the insulation layer. A gas flow guide shield with an adjustable angle is disposed at the opening of the gas inlet, so that the free surface of the melt is blown by the guided gas flow in such a manner that the gas flow takes the impurity away from the free surface efficiently. As a result, the crystal ingot obtained by solidifying the melt will exhibit a reduced concentration of impurities and an improved crystal quality.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a gas supply device for use in a crystal-growing furnace, and more particularly, to a gas supply device for use in a crystal-growing furnace that is capable of effectively reducing the impurities present in the crystal ingot produced thereby.
2. Description of the Prior Art
It is known in the art that a solar cell is a non-pollutant renewable energy source that can directly generate electric power by virtue of the interactions between the sunlight and chemical materials. Especially, the solar cell will not discharge any undesired waste gas during use, such as CO₂, so that the solar cell is promising in helping environmental protection and solving the problem of the earth's greenhouse effect.
A solar cell is a device that is capable of converting the solar energy into electrical power by generating a potential difference at the P-N junction interface of a semiconductor device, rather than by transmission of electrically conductive ions via an electrolyte. The semiconductor device will generate a tremendous amount of electrons when struck by the sunlight, and the movement of the electrons results in a potential difference at the P-N junction.
The modern solar cells are typically made by three types of materials: amorphous materials, mono-crystal materials and poly-crystal materials. FIG. 1 illustrates a furnace for producing a silicon crystal ingot, which primarily includes a crucible 21 for containing a silicon melt 11. The crucible 21 is provided circumferentially with a lateral insulation layer 22 and an upper insulation layer 23, so as to constitute a hot zone, in which a heater 24 are equipped to provide heat to silicon.
The upper insulation layer 23 is further provided with a gas inlet 25 used for introducing an inert gas, whereas the lateral insulation layer 22 may be formed with a gas exit 26. During the process of melting the silicon by heat, a gas is introduced into the furnace at a predetermined flow rate through the gas inlet 25 to generate a gas flow passing through the hot zone and, thus, carrying the impurity away from the furnace via the gas exit 26.
A crystal ingot 12 may be obtained by reducing the output power of the heater 24 (casting process), or by moving the lateral insulation layer 22 upwards to allow radiant cooling of the crucible 21 (directional solidification system process), to thereby solidify the silicon melt 11 contained within the crucible 21.
Moreover, the crystal ingot 12 may also be obtained by additionally disposing a support 28 between the crucible 21 and a base 27, so that the silicon melt 11 contained within the crucible 21 can be solidified by lowering the support 28 to draw the crucible 21 downwards to a cooling zone (Bridgman process), or by introducing a cooling fluid into the support 28 (heat exchanger process).
In the conventional furnace described above, however, the gas inlet 25 of the hot zone device only slightly protrudes into the hot zone beneath the upper insulation layer 23. As a consequence, the opening of the gas inlet 25 is located so far from the free surface of the silicon melt 11 contained in the crucible 21 (namely, the interface of the silicon melt and the gas) that the gas flow introduced through the gas inlet 25 fails to effectively carry the impurities away from the free surface and leads to an unfavorable result that the crystal ingot produced thereby has a high concentration of impurities and a reduced crystal quality.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a gas supply device for use in a crystal-growing furnace that is capable of improving the quality of the crystal ingot produced thereby by effectively reducing the impurities present in the crystal ingot.
In order to achieve this object, a gas supply device for use in a crystal-growing furnace is provided, which comprises an insulation layer enclosing a crucible, a gas inlet mounted in the insulation layer, and a gas exit formed in the insulation layer, so that the gas inlet is allowed to introduce a gas at a predetermined flow rate to generate a gas flow passing through the hot zone and carrying the impurity away from the furnace via the gas exit. Especially, a gas flow guide shield is disposed at the opening of the gas inlet, so that the free surface of the melt is blown by the gas flow guided by the gas flow guide shield. As a result, the crystal ingot thus obtained exhibits a reduced concentration of impurities and an improved crystal quality.
Preferably, the gas supply device according to the invention additionally comprises an adjusting unit coupled to the gas inlet. The adjusting unit allows a precise control of the position of the gas inlet in relation to either the height of crucible or the height of the free surface of the melt during an actual operation, so as to maintain the opening of the gas inlet spaced apart from the free surface of the melt contained in the crucible by a predetermined range of distance. As such, at a given gas flow rate, the impurities can be more efficiently and more rapidly taken away from the free surface of the melt by the gas flow according to the invention disclosed herein as compared to the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and effects of the invention will become apparent with reference to the following description of the preferred embodiments taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating the gas supply device used in a conventional crystal-growing furnace;

FIG. 2 is a schematic cross-sectional view of a furnace according to the first preferred embodiment of the invention;

FIG. 3 is a schematic cross-sectional view of the gas supply device according to the first preferred embodiment of the invention;

FIG. 4 is a schematic diagram showing the adjustment of the gas flow guide shield according to the first preferred embodiment of the invention;

FIG. 5 is a schematic cross-sectional view of the gas supply device according to the second preferred embodiment of the invention;

FIG. 6 is a schematic diagram showing the adjustment of the gas flow guide shield according to the second preferred embodiment of the invention;

FIG. 7 is a schematic diagram showing the contours of the crucible and the guide shield according to the third preferred embodiment of the invention;

FIG. 8 is a schematic diagram showing the contours of the crucible and the guide shield according to the fourth preferred embodiment of the invention; and

FIG. 9 shows the concentration profiles of impurities simulated along the growth direction of grown crystal ingots under different gas inlet designs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a gas supply device for use in a crystal-growing furnace that is capable of improving the quality of the crystal ingot produced thereby by effectively reducing the impurities present in the crystal ingot. As shown in FIG. 2, the furnace according to the invention generally comprises a crucible 31 for containing a silicon melt 41. The crucible 31 is surrounded circumferentially by an insulation layer 32, so as to constitute a hot zone, in which a heater 37 are equipped to provide heat to silicon.
The gas supply device according to the invention comprises a gas inlet 33 protruding from the insulation layer 32, and a gas exit 34 formed in the insulation layer 32, so that the gas inlet 33 is allowed to introduce a gas at a predetermined flow rate to generate a gas flow passing through the hot zone and, thus, carrying the impurity away from the furnace via the gas exit 34. The gas supply device is characterized by the technical features described below.
The gas inlet 33 is provided at its opening with a gas flow guide shield 36 with an adjustable angle for guiding the gas flow from the gas inlet 33 to the regions surrounding the opening of the gas inlet 33, so that the free surface of the melt 41 is blown by the guided gas flow in such a manner that the gas flow takes impurities away from the free surface at a more rapid rate compared to the prior art. As a result, the crystal ingot obtained by solidifying the melt 41 will exhibit a reduced concentration of impurities and an improved crystal quality. Preferably, the crucible 31 is provided above with a cover 39 formed with a gas exit 34, as shown in FIG. 3. As shown in FIGS. 2 and 4, the gas flow guide shield 36 is preferably positioned at an angle between 80˜160 degree, more preferably at an angle of 150 degree, relative to the gas inlet 33.
The furnace that is equipped with the gas supply device according to the invention may be a furnace designed to solidify the melt 41 contained within the crucible 31 by reducing the output power of the heater (casting process), or a furnace designed to solidify the melt 41 contained within the crucible 31 by moving the insulation layer 32 upwards to effect radiant cooling of the crucible 31 (directional solidification system process).
It is apparent to one having ordinary skill in the art that the furnace which is equipped with the gas supply device according to the invention may be additionally provided with a support 38 connected to an underside of the crucible 31, so that the melt 41 contained within the crucible 31 can be solidified by lowering the support 38 to draw the crucible 31 downwards to a cooling zone (Bridgman process), or by introducing a cooling fluid into the support 38 (heat exchanger process). All of the furnaces described herein may be provided with the gas supply device disclosed herein to effectively reduce the concentration of impurities present in the crystal ingot 42 produced by solidifying the melt 41, thereby improving crystal quality of the crystal ingot 42.
Preferably, the gas supply device according to the invention additionally includes an adjusting unit coupled to the gas inlet 33 and used to adjust the position of the gas inlet 33 in relation to the crucible 31. The adjusting unit includes an internally threaded sleeve 35 inserted substantially vertically into the insulation layer 32. The gas inlet 33 is provided on its outer surface with a threaded section 331 for engaging the threaded sleeve 35, so that the relative position of the gas inlet 33 can be adjusted by rotating the gas inlet 33 in relation to the threaded sleeve 35.
By virtue of the arrangement disclosed herein, the inventive gas supply device for use in the furnace allows a precise control of the position of the gas inlet 33 in relation to the height of crucible 31 or the height of the free surface of the melt 41 during an actual operation, so as to maintain the distance between the opening of the gas inlet 33 and the free surface of the melt 41 contained in the crucible 31 within a predetermined range. As a result, at a given gas flow rate, the impurities can be more efficiently and more rapidly taken away from the free surface of the melt 41 by the gas flow according to the invention disclosed herein as compared to the prior art.
In actual practice, As shown in FIGS. 3 and 4, the gas flow guide shield 36 disclosed herein is regularly mounted on the shield body thereof with a plurality of radially arranged rails 361, each connected to the gas inlet 33 via a linkage 362, such that the linkages 362 cooperate with the rails 361 to position the gas flow guide shield 36 at an inclined angle between 80˜160 degree with respect to the gas inlet 33. As shown in FIGS. 5 and 6, the shield body of gas flow guide shield 36 may alternatively be provided with a plurality of hinge elements 363 pivotally connected to the gas inlet 33 in such a manner that the gas flow guide shield 36 is adjusted at an inclined angle between 80˜160 degree with respect to the gas inlet 33, thereby fulfilling the needs of changing the speed of the gas flow.
In addition, as shown in FIG. 7, the guide shield 36 may be configured to have a rectangular outer contour and the crucible 31 is similarly configured to have a rectangular internal contour. Alternatively, the guide shield 36 is configured to have a circular outer contour and the crucible 31 is similarly configured to have a circular internal contour, as shown in FIG. 8. The outer edge of the guide shield 36 is kept apart from the internal wall of the crucible 31 by a predetermined distance.
The gas supply device disclosed herein is tailored to dispose the gas flow guide shield 36 at the opening of the gas inlet 33 to allow the gas flow introduced through the gas inlet 33 to be guided by the guide shield 36, so that the free surface of the melt 41 is blown by the guided gas flow in such an effective manner that the crystal ingot thus produced exhibit a reduced concentration of impurities.
FIG. 9 shows the concentration profiles of impurities measured along the growth direction of grown crystal ingots under different gas inlet designs, in which crystal ingots produced by using a conventional gas inlet design (Test 1) and by using the designs where the gas flow guide shield is positioned with respect to the gas inlet at an inclined angle of 90° (Test 2) and 150° (Test 3), respectively, are subjected to the simulations. At a certain height of grown crystal ingots (for example, at a height of 80 mm along the growth direction), the crystal ingots obtained in Tests 1, 2 and 3 contain an impurity concentration of about 1.6 ppma, 1.25 ppma and 1.05 ppma, respectively. The results indicate that the inventive gas supply device, which is tailored to incorporate a gas flow guide shield, can efficiently enable the production of crystal ingots with a reduced concentration of impurities. Preferred is the design where the gas flow guide shield is positioned at an inclined angle of 150 with respect to the gas inlet.
In conclusion, the gas supply device for use in a crystal-growing furnace as disclosed herein can surely achieve the intended objects and effects of the invention by virtue of the structural arrangements described above. While the invention has been described with reference to the preferred embodiments above, it should be recognized that the preferred embodiments are given for the purpose of illustration only and are not intended to limit the scope of the present invention and that various modifications and changes, which will be apparent to those skilled in the relevant art, may be made without departing from the spirit of the invention and the scope thereof as defined in the appended claims.

Claims

1. A gas supply device for use in a crystal-growing furnace, comprising:

a crucible;

an insulation layer enclosing the crucible and formed with a gas exit;

a gas inlet mounted in the insulation layer and having an opening; and

a gas flow guide shield with an adjustable angle disposed at the opening of the gas inlet.

2. The gas supply device for use in a crystal-growing furnace according to claim 1, wherein the gas inlet is coupled with an adjusting unit for positioning the gas inlet relative to the melt.

3. The gas supply device for use in a crystal-growing furnace according to claim 2, wherein the adjusting unit comprises a threaded sleeve inserted into the insulation layer, and wherein the gas inlet is provided on its outer surface with a threaded section for engaging the threaded sleeve, so that the relative position of the gas inlet can be adjusted by rotating the gas inlet in relation to the threaded sleeve.

4. The gas supply device for use in a crystal-growing furnace according to claim 1, wherein the gas flow guide shield is regularly mounted on its shield body with a plurality of radially arranged rails, each connected to the gas inlet via a linkage.

5. The gas supply device for use in a crystal-growing furnace according to claim 1, wherein the gas flow guide shield is provided on its shield body with a plurality of hinge elements pivotally connected to the gas inlet.

6. The gas supply device for use in a crystal-growing furnace according to claim 1, wherein the gas flow guide shield is configured to have a rectangular outer contour and the crucible is similarly configured to have a rectangular internal contour.

7. The gas supply device for use in a crystal-growing furnace according to claim 1, wherein the gas flow guide shield is configured to have a circular outer contour and the crucible is similarly configured to have a circular internal contour.

8. The gas supply device for use in a crystal-growing furnace according to claim 1, wherein the crucible is provided above with a cover formed with a gas exit.